This invention relates generally to a technique for applying a sealant to the threads of a fastener for providing a fluid-tight seal when threadedly engaged with a mating threaded element, as well as a device for carrying out such technique. More particularly, this invention relates to such a method and device wherein the sealant is pressed into the thread roots of the element, and differently sized elements are capable of being coated without changing applicators.
Prior known techniques in the application of sealant, especially of the anaerobic adhesive type, to the threads of female threaded fasteners are beset with problems in failing to meet quality control standards such as the avoidance of air bubbles during the application process. Otherwise, it has been difficult to control the requisite quantity of sealant to be coated without giving a sloppy appearance and without applying more than as needed. On the other hand, known sealant applying and coating devices for threaded fasteners, while better suited for controlling the desired amount of sealant applied to the threads, are not without their shortcomings. Air bubbles quite often remain entrapped in the applied sealant, resulting in a weakened seal and/or lock between the coated fastener and its mating part. Besides, the nozzle or sealant applicator used in the application process must be replaced with an appropriately sized applicator each time a differently sized threaded element is to be coated.
Examples of these prior art devices are disclosed in U.S. Pat. No. 3,956,533 to Weber et al, Gebrauchsmuster 7930867.1, and in U.S. Pat. No. 3,416,492 to Greenleaf. In the Weber et al and German patents the applicator is in the form of a threaded plug which engages the threads of a female threaded element to be coated. With such a screw threading coating operation, however, the threads are either incompletely covered with sealant and/or formation of air bubbles is difficult to avoid because of the inability to press the sealant in place. Moreover, differently sized female threaded elements having differently sized threads require complementarily sized threaded applicators, and repeated use of the same threaded applicator for the same sized elements oftentimes results in an undue buildup of sealant on the applicator threads.
In the aforementioned Greenleaf patent, use of such a coating nozzle renders it impossible to precisely control the amount of product to be coated or to effect a pressing of the coating in place against the threads. And, other problems mentioned above are not avoided by this coating approach.